Hi,
No, the Schema.org generator is not enabled by default.
It is strange how the plugin interferes with the feed. I'll do some thorough testing in a few hours.
Do you have access to the web server's error log? Since this is a 500 error, there should be a PHP error message in there at the time the feed is accessed. If available, that message would be very helpful for me in order to determine what could possibly be wrong.
George